Application Layer Gateway (Alg); Overview - D-Link DFL-1600 User Manual

Application Layer Gateway
18.1

Overview

To complement the limitations of packet filtering, which only inspect in the
packet headers, such as IP, TCP, UDP, and ICMP headers, D-Link firewalls
embed an Application Layer Gateway (ALG) to support higher level
protocols that have address information within the payload.
The ALG acts as the user's representative to obtain most commonly used
Internet applications outside the protected network, e.g. Web access, file
transfer, and multimedia. Such application-aware agents provide higher
security than packet-filtering-only firewalls, since they are capable of
scrutinizing all traffic for specific service protocols to give protection at the
top level of the TCP/IP stack.
In this chapter, the following application standards supported by D-Link
ALGs are described.
FTP
HTTP
H.323
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(ALG)